High dropping point complex grease

ABSTRACT

A TOW-STEP PROCESS FOR PREPARING A HIGH TEMPERATURE GREASE IS PROVIDED, IN WHICH A THICKENING AGENT IS FIRST FORMED, IN THE FIRST STEP, BY NEUTRALIZING A LOWER ALKYL ESTER OF A HYDROXY FATTY MONOCARBOXYLIC ACID WITH AN EXCESS OF A METAL BASE SELECTED FROM THE GTOUP CONSISTING OF ALKALI METAL BASES AND ALKALINE EARTH METAL BASES IN AN OIL VEHICLE. THE REACTION IS CONDUCTED AT ELEVATED TEMPERATURE IN THE RANGE OF 300* TO 400*F. IN A CLOSD SYSTEM. IN THE SECOND STEP, AN ALKYL ESTER OF AN ALIPHATIC DICARBOXYLIC ACID IS ADDED TO THE SOAP-THICKENED OIL COMPOSITION OF STEP ONE. THE MIXTURE THUS FORMED IS HEATED TO A TEMPERATURE IN THE RANGE OF 350* F. TO 450* F. IN A CLOSED SYSTEM.

United States Patent O 3,809,650 HIGH DROPPING POINT COMPLEX GREASE Francis S. Sayles, Rocky Hill, N.J., assignor to Mobil Oil Corporation, New York, N.Y. No Drawing. Filed June 16, 1971, Ser. No. 153,852 Int. Cl. C10m 5/14, 5/16, 7/22 US. Cl. 252-42 7 Claims ABSTRACT OF THE DISCLOSURE A two-step process for preparing a high temperature grease is provided, in which a thickening agent is first formed, in the first step, by neutralizing a lower alkyl ester of a hydroxy fatty monocarboxylic acid with an excess of a metal base selected from the group consisting of alkali metal bases and alkaline earth metal bases in an oil vehicle. The reaction is conducted at elevated temperature in the range of 300 to 400 F. in a closed system. In the second step, an alkyl ester of an aliphatic dicarboxylic acid is added to the soap-thickened oil composition of step one. The mixture thus formed is heated to a temperature in the range of 350 F. to 450 F. in a closed system.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to lubricating grease compositions and, in one of its aspects, relates more particularly to lubricating grease compositions of increased dropping points and especially suited for lubrication under high temperature conditions. Still more particularly, in this aspect, the invention relates to an improved process for the preparation of the aforementioned high temperature lubricating greases.

(2) Description of the prior art The prior art provides processes in which lubricating greases are prepared by neutralizing a fatty monobasic acid with a metal base in a lubricating oil vehicle, in a single-step operation. Such grease formulations have, in many instances, been found to result in greases having relatively low dropping points and which are also incapable of withstanding relatively high temperature applications for extended periods of time. Hence, in accord ance with present day requisite, greases having relatively high dropping points and which are particularly suited for high temperature applications, are highly desirable.

SUMMARY OF THE INVENTION In accordance with the present invention, and in accordance with its objects, there are provided improved greases of relatively high dropping points and high temperature application capability, prepared in a two-step process, which comprises (A) in a closed system, reacting an ester of a fatty monocarboxylic acid having from about 12 to about 22 carbon atoms with a metal base, in a lubricating oil vehicle, in an amount sufiicient to neutralize the ester to form a metal soap of the fatty monocarboxylic acid and to thicken the oil, the reaction being conducted at a temperature from about 300 F. to about 400 F. and preferably from about 340 F. to about 360 F.; (B) adding to the thus soap-thickened oil a diester of a dicarboxylic acid having from about 4 to about carbon atoms in an amount sufficient to raise the dropping point of the thickened oil; and (C) subjecting the mixture thus formed to a temperature from about 350 F. to about 450 F. and preferably from about 400 F. to about 415 F. in a closed system for a time suflicient to form a complexed grease composition.

In preferred embodiments, the novel grease compositions of the present invention comprise from about 72 to about 96%, by weight, of the lubricating oil vehicle and from about 4 to about 28%, by weight, of thickener. In such preferred formulations, the thickener may comprise from about 3 to about 12%, by weight, of an ester of a fatty monocarboxylic acid neutralized with about 0.6 to about 5.6%, by weight, of the metal base and from about 0.3 to about 10%, by weight, of the diester of the dicarboxylic acid. Also, in such preferred formulations, the ratio of the metal soap formed to the metal salt of the dicarboxylic acid is preferably within the range from about 9:1 to about 1:1.

Insofar as the oil vehicle is concerned, any oil of lubricating viscosity can be employed. Such oils may therefore include mineral oils or synthetic oils of wide varieties and types normally employed in the manufacture of lubricating grease compositions.

Thus, mineral oils having a viscosity of at least 40 SUS at 100 F., and particularly those falling within the range from about 60 SUS to about 6,000 SUS at 100 F. may be employed. In instances, where synthetic vehicles are employed rather than mineral oils, or in combination therewith, as the lubricating vehicle, various compounds of this type may be successfully utilized. Typical synthetic vehicles include: polypropylene glycol, trimethylol propane esters, neopentyl and pentaerythritol esters, di- (2-ethyl hexyl) sebacate, di-(2-ethyl hexyl) adipate, dibutyl phthalate, fiuorocarbons, silicate esters, silanes, esters of phosphorus-containing acids, liquid ureas, ferrocene derivatives, hydrogenated mineral oils, chain-type polyphenyls, siloxanes and silicones (poly-siloxanes), alkyl-substituted diphenyl ethers typified by a butyl-substituted bis (p-phenoxy phenyl) ether, phenoxy phenyl ethers, etc. The metal base employed for reaction with the ester of the fatty monocarboxylic acid may include the metals normally used in the manufacture of grease thickeners. Particularly preferred are the alkali metal, the alkaline earth metal hydroxides or oxides and mixtures of alkali and alkaline earth metals, and may be employed either in the form of their hydrates or as water solutions thereof. If so desired, additional additive materials such as stabilizers, antioxidants, anti-wear agents and extreme pressure agents commonly employed in grease formulations may be added to form the final grease product.

The above-described feature of employing a two-step process makes possible a controlled rate of complexing so that a grease of increased structural stability at high temperature and increased dropping point is obtained.

The following examples and comparative data will serve to illustrate the novel grease compositions of the present invention and their superior characteristics when formed in accordance with the above-described two-step process.

DESCRIPTION OF SPECIFIC EMBODIMENTS In the examples of the following table, the above-described two-step process was carried out, in each instance, in which the indicated thickening agent was first formed by neutralizing the methyl ester of l2-hydroxystearic acid with an excess of lithium hydroxide monohydrate in a lubricating oil menstruum. The lubricating oil used was a solvent refined 500 SUS at 100 F. naphthenic oil. The above-described mixture was then subjected to pressure saponification, heated to 350 F. and the internal pressure thus formed was then released. In the second step, further dilution by a solvent refined SUS at 210 F. parafiinic bright stock of the formed soap-oil mixture was carried out, followed by the addition of the diester of a di-carboxylic acid, viz dimethyl azelate. The pressure vessel was again closed and heated to 410 F. Internal pressure was then released and the resulting product was then discharged to a finishing kettel where cooling, addition of additives and homogenization was carried out. In each of 3 the examples disclosed in the table, the antioxidant comprised 3%, by weight, of a polymerized trimethyl dihydroquinoline and 0.2%, by weight, of a modified long chain fatty acid irnidazoline rust inhibitor.

As will be seen from the foregoing table, the grease of Example 1, prepared in a single-step operation without the presence of the aforementioned diester of a dicarboxylic acid, exhibits a dropping point of only 384 F. On a comparative basis, however, the greases of Examples 2 through 5, prepared in a two-step operation, in accordance with the present invention, and employing a diester of a dicarboxylic acid in the second step (represented by the dimethyl azelate) exhibited markedly increased dropping points ranging from 491 F. to 544 F.

It should be noted that other esters of fatty monocarboxylic acids having from about 12 to about 22 carbon atoms can be substituted in the above-described examples, if so desired. These may include: hydrogenated castor oil, hydrogenated tallow glycerides, and others commonly used in making lubricating grease thickeners. Other metal bases may also be employed, including those commonly used in making lubricating grease thickeners such as caustic soda and lime. With respect to the diester of the dicarboxylic acid having from 4 to 10 carbon atoms, in addition to dimethyl azelate, other diesters may be employed including: dimethyl succinate, dimethyl adipate, dibutyl sebacate, di-2-ethyl hexyl sebacate and dimethyl sebacate.

Although the present invention has been described herein by means of certain specific embodiments and illustrative examples, it is not intended that the scope thereof be limited in any way, and is capable of various modifications and adaptations as those skilled in the art will readily appreciate.

I claim:

1. A method for preparing a lubricating grease composition which comprises:

(A) in a closed system, reacting a lower alkyl ester of a hydroxy fatty monocarboxylic acid having from about 12 to about 22 carbon atoms with an excess of a metal base selected from the group consisting of alkali metal bases and alkaline earth metal bases, in a lubricating oil vehicle, in an amount sufiicient to neutralize said ester to form a metal soap of said fatty monocarboxylic acid and to thicken said oil, said reaction being conducted at a temperature from about 300 F. to about F.

4 (B) adding to the thus-thickened oil an alkyl diester of an aliphatic dicarboxylic acid having from about 4 to about 10 carbon atoms in amount sufiicient to raise the dropping point of said thickened oil; and

(C) subjecting the mixture thus formed to a temperature from about 350 F. to about 450 F. in a closed system for a time sufiicient to form a complexed grease composition wherein the ratio of the metal soap of the hydroxy fatty acid to the metal salt of the dicarboxylic acid is within the range of from about 9:1 to about 1:1.

2. A method as defined in claim 1 wherein the temperature employed in (A) is within the range of from about 340 F. to about 360 F.

3. A method as defined in claim 1 wherein the temperature employed in (C) is within the range from about 400 F. to about 415 F.

4. A method as defined in claim 1 wherein said lubricating grease composition comprises from about 72 to about 96%, by weight, of said lubricating oil and from about 4 to about 28%, by weight, of said thickener.

5. A method as defined in claim 1 wherein said thickener comprises from about 3 to about 12%, by weight, of said ester of a fatty monocarboxylic acid neutralized with about 0 .6 to about 5.6%, by weight, of said metal base; and from about 0.3 to about 10%, by weight, of said diester of a dicarboxylic acid.

6. A method as defined in claim 1 wherein said oil vehicle comprises a mineral oil; said ester of a monocarboxylic acid comprises methyl 12-hydroxystearate; said diester of a dicarboxylic acid comprises dimethyl azelate; and said metal base comprises lithium hydroxide monohydrate.

7. A lubricating complexed grease composition comprising an oil of lubricating viscosity as a vehicle and a thickener comprising a metal soap of a fatty monocarboxylic acid having from about 12 to about 22 carbon atoms and a metal salt of a dicarboxylic acid having from about 4 to about 10 carbon atoms and prepared in accordance with the method of claim 1.

References Cited UNITED STATES PATENTS 3,585,138 6/1971 Boehringer et al 252-42 3,200,073 8/ 1965 Criddle 25242 2,583,607 1/ 1952 Sirianni et a1. 252-41 2,710,838 6/ 1955 Morway et a1 25241 2,859,179 11/1958 Lux et a1 252-41 2,898,296 8/1959 Pattenden' et a1. 252-41 2,940,930 6/1960 Pattenden et al. 252-41 3,681,242 8/ 1972 Gilani et a1 25241 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. 01. X.R. 252-41, 52 R 

